1. Field of the Invention
The present invention relates to an air flow control valve means and, more particularly, to an air flow control valve means for use in air bleed control in carburetors.
2. Description of the Prior Art
Hitherto, it has been proposed to control the air-fuel ratio of a mixture to be fed to an automotive engine by controlling the amount of air bleed to the carburetor. This air bleed control is achieved by opening and closing an air bleed passage by means of a control valve disposed at an air inlet end of the air bleed passage.
Some of the control valves used in air bleed control have an air flow passage opening adapted to be opened and closed by a valve element, and a bypass air passage having a smaller opening area than the above-mentioned opening which is continuously open to prevent fuel from flowing back through the air bleed passage when the first-mentioned opening is closed. In such a control valve, the bypass air passage is constructed to have an extremely small opening area in order to minimize the change in the rate of air bleed effected by the air flowing out of the bypass air passage. Therefore, the bypass air passage tends to become clogged with dust and other foreign material. This problem is serious particularly when the bypass air passage opens to the bottom portion of the valve housing, because, in such a case, the dust and foreign material falling onto the bottom wall of the valve housing tend to come into the opening of the bypass air passage together with the rain water or the like introduced into the valve housing. It is, therefore, extremely difficult to ensure safe operation of the bypass air passage for long periods of time without suffering clogging.